Balls are used in wellbores for a number of purposes. For example, balls may be deployed to operate various downhole tools, such as packers, cross-over tools, valves, etc. In a particular example, different-sized balls 10 as shown in FIG. 1 may be deployed to open sliding sleeves on a tubing string to perform treatment operations at various zones of the wellbore.
The balls 10 can be composed of a number of suitable materials 16 and may be subjected to various types of conditions (pressures, temperatures, fluid compositions, etc.). Aluminum balls are used in some applications, while composite balls are used in others. Some balls may even be composed of dissolvable materials so that the balls degrade in the wellbore environment overtime when exposed to temperatures, fluids, or other conditions.
In plug and perforation operations, a ball 10 is deployed downhole to close the fluid passage in a bridge plug so fracture treatment can be applied through perforations in casing. This can be repeated multiple times up the borehole as perforations are made in the casing and lower zones are sealed off by bridge plugs. Once operations are complete, all of the bridge plugs and balls 10 in the casing are milled out.
In a facture operation, balls 10 having successively increasing sizes are deployed downhole to actuate sliding sleeves on a tubing string. Thus, a smaller ball 12 is deployed downhole to open a sliding sleeve and close off fluid communication further downhole on the tubing string before a lager ball 14 is deployed to open another sliding sleeve further uphole. The configuration of ball sizes and seats ensures that a deployed ball 10 having a particular diameter engages a particular seat configured in one of the sliding sleeves so pressure applied behind the seated ball can open the sleeve.
With a ball 10 seated in the open sleeve, increased tubing pressure and treatment fluid are diverted out of the open sleeve to treat the surrounding zone in the wellbore. Once operations are complete, the multiple balls 10 in the sliding sleeves can be floated to the surface, and any balls 10 remaining downhole may be milled out.
As can be seen in both of the above examples, the balls 10 used downhole in some applications are preferably composed of a millable material, such as a composite material, which can be ground to pieces during milling operations. Yet, to operate properly, the composite balls need to withstand high fracture pressures and need to maintain their shape engaging the seats under such pressures. If the ball deforms or fails, then the fluid seal it provides with the seat will be compromised and make the fracture treatment ineffective.
As the industry progresses, higher pressures are being used downhole, and more and more treatment zones are being used downhole in a given wellbore. Existing composite fracturing ball technology is approaching a pressure and temperature limitation beyond which composite balls become less effective. Conventional manufacturing methods mold each ball from the desired material 16 or machine each ball to the appropriate form from a blank of the desired material 16. Both of these methods have limitations as to what strength the balls 10 can achieve.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.